Projection means



Jan. 10, 1939. P T. FARNSWORTH PROJECTION MEANS Original Filed Nov. 6,1934 w m HM T w INVENTOR, PH/LO. r. FARNSWORT BY M W T ATTORNEYS.

Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE PROJECTION MEANS niaOriginal application November 6, 1934, Serial No. 751,716. Divided andthis application July 1,

1935, Serial No. 29,243

5 Claims.

My invention relates to apparatus for the projection of motion pictures,and particularly tosuch apparatus adapted to be used in conjunction witha television transmitter; this application being a division of myco-pending application, Serial No. 751,716, filed November 6, 1934, forprojection apparatus.

Among the objects of my invention are: To provide, in motion pictureprojection, a shutter which permits a longer interval of exposure ofpicture areas between periods when the light beam is cut off to permitshifting of the film; to provide a shutter which, when operated with aprojector having a moderate speed film shifting mechanism, produces theeffect of a high speed mechanism, by shortening the cut-off period be-,tween successive exposures of the film; to provide, in apparatus of thecharacter described, projection means for a motion picture film, which,while operable to project a series of images considerably in excess ofthe frequency necessary to maintain persistency of vision, will produceintervals of exposure of each image equivalent to that obtainable withsuch a frequency without introducing the objectionable flickeridentified therewith; to provide a simple and easily constructedshutter, and one which may be constructed from readily procurablematerials; to provide a shutter which maintains portions of a projectedimage in stationary relationship to a screen even though the film fromwhich the image is projected is moving; to provide means for refractinga beam of light projected from a source to a screen through means fordefining the cross sectional shape of the beam, so that portions of thedefined area of the beam projected on the screen will remain stationarywhen the beam-defining means is moved transverse to the axis of thebeam; and to provide improved projectors for use with moving picturefilm.

Other objects of my invention will be apparent or will be specificallypointed out in the description i otming a part of this specification,but I do not limit myself to the embodiment of the invention heeindescribed, as various forms niay be adopted ithin the scope of theclaims.

Referring to the drawing:

Figure 1 is an elevational view, mostly diagrammatic in character andreduced to lowest terms, of a system incorporating the improvedprojection apparatus of my invention.

Figures 2 to 5 inclusive are diagrammatic views illustrating the meansfor retracting the projected light beam in different stages ofarrangement.

Stated broadly, my invention comprises the combination, with apparatusfor projecting in rapid sequence, a series of optical images on asurface from a motion picture film, or other means for defining theimage, including means for intermittently moving elemental portions ofsaid film or image-defining means into registry with a beam of lightemanating from a light source and projected on said surface, andallowing said elemental portions to dwell for intervals in said beam,and a shutter for intersecting said beam at other intervals to obstructpassage of portions of the beam to the surface during movement of thefilm; of means operating in conjunction with said shutter for refractingportions of the beam so that portions of the area illuminated by thebeam on the surface will remain in stationary relationship theretoduring a portion of the movement of the film or beam-defining means.

At the present time extensive research work is being carried on in thefield of the transmission of motion pictures by television. Heretofore,it has been the practice to utilize a standard motion picture projectorfor reproducing successive optical images from the motion picture film,which images may be scanned, in succession, by any of the severalmethods of scanning well known in the television art, to produce a trainof television signals.

Most modern projectors, due to sound track requirements, are designed toshift the film intermittently at the rate of twenty-four picture framesper second and allow, in these intervals, for equal periods of exposureand concealment of the film; i. e., each picture frame will be uncoveredby the projector shutter, to permit passage of the light beam, forone-forty-eighth of a second, and for a similar period will be coveredby the shutter during shifting of the film to allow movement of thesucceeding picture frame into registry with the light beam. It will beseen, therefore, that in televising a single image, a complete scansionthereof must occur within that fraction of a second comprising thestationary period. This means that, in order to produce a televisionimage possessing the number of picture elements of a size necessary tobring out the fine detail of the image, the length of time that eachelement of the image is exposed to the scanning means is exceedinglyshort, due to the speed at which the scanning means must travel in orderto cover the exposed image in the allotted time. The overall time of acomplete film cycle cannot be changed, due to the second requirement ofa ninety feet per minute rate of progression.

I have found that, without material alteration, the standard motionpicture projector can be made to increase the time available forscansion without changing the existing ratio between the intervals ofmovement and rest of the film, and that the time between scansions maybe decreased accordingly. This is accomplished by providing a shutter,including a prism of material permeable to light in one dimension androtatable in synchronism. with the movement of the film. This prismoperates during the portions of time when the film is moving to refractthe light beam and displace a portion of the projected image withrespect to the picture on the film so that it is in position to bescanned before the film comes to rest in the light beam, and similarlyto maintain a portion of the image in position when the film againstarts to move. This means that scansion of the image may start beforethe film comes to rest and may continue after the film has started tomove to bring the next succeeding picture frame into registry ,with thelight beam.

In greater detail, the apparatus shown in Figure 1 represents apparatus,including one preferred form of the shutter of my invention, which maybe used to transmit motion pictures by television. The film 2, depictingthe action to be transmitted, is moved, by the intermittent sprocket 3,in the usual successive increments past the aperture 4, formed in aplate 5, which defines the light beam 6 emanating from the source 1 andpassing through the condensing lens 8. An objective lens system 9 isprovided in the path of the light beam for focusing the beam beforesuitable scanning apparatus.

This is accomplished by providing a gear 21 which is fixed on the shaftcarrying the intermittent sprocket 3, which gear is in mesh,

' through an idler gear 28, with a pinion '29. The

the shifting of each successive picture frame of Referring now to thediagrams shown in Figures 2 to 5 inclusive, we find that, in Figure 2,the positions of the elements are the same as in Figure 1, whichposition they occupy during each exposure of the film. The film in thesediagrams is indicated by a series of joined arrows, the distance betweenthe points thereof representing the length of each picture frame. Thelight beam 6 has been shown as comprising four parallel zones which willbe useful in describing the operation of the shutter and prism to beexplalned directly. The objective lens system 9, of Figure 1, has beenreplaced, in the diagrams,

with an apertured plate 34, similar to the plate 5,

so that the deflection of the light beam may be more readily understood.

In Figure 3 the film has started to move downwardly, to bring a newpicture frame into position before the aperture 4, and the shu te hasrotated so that the leading edge of the upper portion of the framethereof has advanced into registry with the receding edge of thepreviously exposed picture frame. As the prism rotates, from theposition shown in Figure 2 to that shown in Figure 3, the angle of theprism faces, with respect to the axis of the beam, progressively changedwith the result that the beam was refracted in passing through the prisman amount corresponding to the distance that the picture frame had beendisplaced with respect to the aperture d. This progressively increasingrefraction of the beam maintained the optical image in the samerelationship with the aperture in the plate 34 as existed when the filmframe was positioned directly before the aperture 4. Further movement ofthe film and consequently rotation of the shutter frame will cause thelight beam to be cut oil, as shown in Figure 4; and continued movementof the elements will create a condition which is shown in Figure 5; thisbeing the reverse of what occurred during movement of the shutter frameto the position shown in Figure 3, in that the leading edge of the nextsucceeding picture frame of the film has been refracted so that thatportion of the picture exposed through the prism is already alined withthe aperture in the plate 34 even though the picture frame has not yetmoved into alinement with the aperture 4. It will be readily seen byexamination of the diagrams that exactly a fifty percent increase in theexposure time of each picture frame is obtained between the cut-off ofthe image, as shown in Figure 3, and the start of exposure of the image,as shown in Figure 5. It will also be seen that a reduction of likepercentage is obtained in the dark period between exposures ofsuccessive picture frames of the film.

The improved shutter just described is characterized by simplicity, easeof construction, and ready applicability to existing motion pictureprojectors for the uses described above.

I claim:

1. The combination, with apparatusfor projecting successive opticalimages from a motion picture film, of intermittent driving means sopositioned and arranged as to maintain said film stationary before saidprojecting means for a definite interval of time, and to draw successiveframes of said film into position during equal intervals of time, of alight-pervious prism and means associated with said film-driving meansfor rotating said prism one-half revolution for each one-frame advanceof said film and in synchronism therewith, said prism being soconstructed and arranged as to maintain the projected image of a portionof said film frames in a fixed position during the movement of saidframes into andout of position before said projecting means.

2. The combination, with apparatus for projecting successive opticalimages from'a motion picture film, of intermittent driving means sopositioned and arranged as to maintain said film stationary before saidprojecting means for a definite interval of time, and to draw successiveframes of said film into position during equal intervals of time, of alight-pervious prism and means associated with said film-driving meansfor rotating said prism one-half revolution for each one-frame advanceof said film and in synchronism therewith, said prism being soconstructed and arranged as to project the image of the leading edge ofeach film frame in a desired position while said frame is being drawninto position, and to project the image of the trailing edge of saidframe in a desired position as said film is moved to present the nextsuccessive film frame to said projecting means.

3. The combination, with apparatus for projecting optical images fromsuccessive frames of a motion picture film, of film-driving means, aplano-parallel light-pervious prism, having one pair of oppositelydisposed faces opaque, rotatably mounted between said film and saidprojecting apparatus, a driving mechanism connected to said film-drivingmeans and to said prism so constructed and arranged as to move said filmand said prism intermittently in synchronism, at the rate of one-halfrevolution of said prism to one film frame advance and to maintain saidfilm and said prism at rest between said intermittent movements, saidprism being dimensioned to project in normal position the leadingportion of each film frame during the movement of said frame intoposition before said projecting means, and to project in normal positionthe trailing portion of said frame during movement of said frame out ofposition before said projecting means.

4. The combination, with apparatus for projecting successive opticalimages from a motion picture film including means for intermittentlymoving said film through a beam of light, of a shutter comprising atubular opaque frame mounted rotatably in said beam of light, sopositioned and arranged as to occult said beam during a portion of itsangular rotation, and to pass said beam during the remaining portion,means driven by said film moving means for rotating said frame insynchronism therewith, one-half revolution for each one-frame advance ofsaid film, and means mounted in said frame for refracting the image ofsaid film frame at the beginning and end of said intermittent filmmovements by an amount suflicient to produce a stationary projectedimage thereof during the periods immediately prior and subsequent tosaid film movements.

5. The combination, with apparatus for projecting successive opticalimages from a motion picture film including means for intermittentlymoving said film through a beam of light, of a shutter comprising atubular opaque frame mounted rotatably in said beam of light, sopositioned and arranged as to occult said beam during a portion of itsangular rotation, and to pass said beam during the remaining portion,means driven by said film moving means for rotating said frame insynchronism therewith, one-half revolution for each one-frame advance ofsaid film, and a light pervious prism mounted in said frame, soproportioned as to refract the projected image of said film by an amountsulficient to produce a stationary projected image during the periodsimmediately prior and subsequent to stationary periods in said filmmovements.

PHILO T. EARNSWORTH.

